High speed Diesel-type engines are well known for their durability under severe operating conditions. Because of this, they have found favor for use in large, heavy-duty motor vehicles, such as trucks, buses, and in locomotives. Recently, however, the use of this type of engine in light-duty road vehicles, such as passenger cars, has begun to increase sharply, this is due largely to industry attempts to achieve increased fuel ecomony. One particular problem associated with the use of diesel engines, however, is the emission of particulate matter derived from the heavy motor fuels containing low volatility ends on which these engines operate. Accordingly, as these engines become more widely used in light-duty road vehicles, a method for reducing the amount of particulate emissions that accompany their operation would be very desirable.
In accordance with the present invention, it has now been found that certain organic nitrates when added in combination with a cyclopentadienyl manganese tricarbonyl to liquid hydrocarbon fuels unexpectedly cooperate to reduce the particulate emitting tendencies of these fuels.
It is known that cyclopentadienyl manganese compounds are excellent antiknocks in gasoline used to operate internal combustion engines and have proven to be especially beneficial in solving some of the problems associated with the use of low-lead or lead-free gasoline in internal combustion engines. Use of such compounds as antiknocks is described in U.S. Pat. Nos. 2,818,417; 2,839,552, and 3,127,351, all incorporated herein by reference.
It is also known that the ignition quality of diesel fuels can be increased by the addition thereto of certain organic nitrate compounds. For example, U.S. Pat. No. 2,280,217 discloses an improved fuel for compression-ignition engines of the Diesel-type which comprises a hydrocarbon fuel having a flash-point above 150.degree. F. and a small amount of an alkyl nitrate having at least 10 carbon atoms per molecule. U.S. Pat. No. 2,031,497 discloses a compression-ignition fuel comprising a fuel oil boiling above the gasoline range containing the nitrates of the mixture of open branched chain aliphatic monohydric alcohols obtainable by the catalytic hydrogenation of carbon monoxide and having at least 4 carbon atoms and containing isobutyl alcohol. U.S. Pat. No. 2,324,779 teaches the use of alkyl nitrates containing 3-6 carbon atoms per molecule as having ignition acceleration effects when used in motor fuels. U.S. Pat. No. 2,618,650 discloses the use of nitrate esters of the isomeric amyl alcohols as being effective for increasing the ignition quality of diesel fuels. U.S. Pat. No. 3,001,857 discloses a composite diesel additive consisting of a blend of a high-grade hydrocarbon diesel oil and a substance selected from a group of substances consisting of alkyl nitrates and N-alkyl, N-nitro and alkyl carbamates. U.S. Pat. No. 2,905,540 discloses the use of nitric acid esters of hydroaromatic or cycloaliphatic alcohols in diesel fuels to increase the cetane number of such fuels. U.S. Pat. No. 3,415,632 discloses a fuel oil composition containing a combination of cyclohexylnitrate and an oil-soluble barium salt of a sulfonic acid to inhibit exhaust smoke emission. U.S. Pat. No. 2,158,050 teaches the use of C.sub.1 -C.sub.5 alkyl nitrates as cetane improvers.
It has now been found that when organic nitrates of the aforediscussed type, which have previously found use as ignition accelerators in diesel fuels, are added to liquid hydrocarbon fuel in combination with a cyclopentadienyl manganese tricarbonyl an unexpected reduction in the particulate emitting tendencies of the composite fuel is obtained.